This invention relates to communication systems for transferring information between a moving vehicle and a stationary location.
Systems are known which provide the capability of exchanging information between a stationary location and a moving vehicle, such as an automobile, truck, bus, emergency vehicle or a railroad car. Such systems typically employ either some type of modulated or encoded light radiation (such as the light based vehicle preemption system) or r.f. signals encoded with appropriate information and transmitted using appropriate transmitting and receiving antennae. An example of the latter type of communication system is described in U.S. Pat. No. 3,609,247 issued Sept. 28, 1971. Such known systems have been proposed for use, and in many cases actually used, in a wide variety of signalling applications. Examples of such applications are preempting the normal traffic intersection signal light control sequence in favor of an emergency vehicle (such as a fire truck, ambulance or police car); detecting the identity of railroad cars, buses and other vehicles passing a particular location; and a wide variety of other vehicle identification and control functions.
Aside from the expected technological difficulties in designing and implementing useful communication systems involving a stationary component and a moving component, perhaps the major deterrent factor to the wide spread implementation of vehicle-stationary location communication systems has been the cost of installing and maintaining the stationary location antenna element. The inductively coupled system shown in the above-referenced '247 U.S. patent, for example, requires the installation of a specially designed coaxial trunk cable along the roadbed to enable the communication of information between the moving vehicle and the stationary sites. Other systems employ transmitting/receiving antennae mounted in roadside boxes, which are not only costly to erect but also vulnerable to vandalism. Still other systems employ inductive loops permanently embedded in the roadbed or along the edge of the roadbed, which are specially designed for use in the communication system. Such embedded loop antennae are extremely costly to install, and the installation process usually results in the disruption of vehicular traffic and danger to the workmen performing the installation.
Efforts in the past to provide a vehicle communication system devoid of the above disadvantages have not met with success.